1. Field of the Invention
The present invention relates to a solid-state imaging apparatus used for image reading apparatuses, such as a copier and a scanner.
2. Description of the Related Art
As image reading apparatuses, such as a copier, what reads both of a monochromatic image and a color image has spread. In recent years, there is a sensor having one line of cells for monochromatic image reading in addition to pixel (color pixel) columns for three lines corresponding to respective color components of R (red), G (green) and B (blue) as a solid-state imaging apparatus mounted in these image reading apparatuses. That is, sensors with 4-line construction which have a pixel (monochrome pixel) column for one more line for monochromatic image reading have been used. As these sensors, for example, construction shown in FIG. 2 in Japanese Patent Application Laid-Open No. 2003-087503 or FIG. 6 in Japanese Patent Application Laid-Open No. 2003-007996 is mentioned.
In addition, there is construction shown in FIG. 13 in Japanese Patent Application Laid-Open No. H06-204445 as an example of a four-line sensor which performs charge-voltage conversion for every pixel in a post-stage of a photoelectric conversion element represented by a MOS type. That is, besides the photoelectric conversion element and charge-voltage conversion unit, it includes a signal hold capacitor for every pixel and a capacitor writing switch to the signal hold capacitor, and a common output line for every color and an output transfer switch of every pixel to the common output line. Furthermore, it is constructed of a shift register, which scans every pixel, and open and close each transfer switch to a horizontal output line, and each output unit for every color. In addition in the subject, it has construction of having not only RGB pixels, but also photoelectric conversion elements for non-visible light.
In addition, when performance improvement such as improvement in an S/N ratio is required, circuitry of a sensor as shown in Japanese Patent Application Laid-Open No. 2006-211363 may be adopted. The circuitry in FIG. 1 of Japanese Patent Application Laid-Open No. 2006-211363 has another line of holding capacitors besides one line of signal holding capacitors, and another line of holding capacitors holds noise components generated in the photoelectric conversion element for every pixel and the charge-voltage conversion unit.
Then, in the output unit including a differential amplifier, the noise component is removed by taking difference between the signal component held and noise component held by each holding capacitor. In addition, there may be construction of having a gain amplifier in a pre-stage of two holding capacitors as showed in FIG. 1 of Japanese Patent Application Laid-Open No. 2003-051989 for improvement in an S/N ratio.
In conventional image reading apparatuses, as described in Japanese Patent Application Laid-Open No. 2003-087503, since only color pixel signals are used at the time of color image reading, constituent elements such as an output unit, a holding capacitor, and a gain amplifier which are connected to a monochromatic pixel column in the solid-state imaging apparatus with 4-line construction are not used. Thus, they consume vainly electric power of each constituent element connected to the monochromatic pixel column at the time of color image reading.
Similarly, they consume vainly electric power of each constituent element connected to the color pixel column also at the time of monochromatic image reading. In addition, since each constituent element which is not needed at the time of each image reading is arranged, it becomes a factor of consuming a useless area and a factor of cost hike of a sensor.